The skeletal system includes many long bones that extend from the human torso. These long bones include the femur, fibula, tibia, humerus, radius and ulna. These long bones are particularly exposed to trauma from accidents, and, as such, may be fractured during a trauma. Automobile accidents, for instance, are a common cause of trauma to long bones. In particular, the femur and tibia frequently fracture when the area around the knee is subjected to a frontal automobile accident.
Often the distal end or proximal portions of the long bone, for example the femur and the tibia, are fractured into several components and must be realigned. Mechanical devices, commonly in the forms of pins, plates, screws, nails, wires and external devices are commonly used to attach fractured long bones. The pins, plates, wires, nails and screws are typically made of a durable material compatible to the human body, for example titanium, stainless steel or cobalt chromium.
Subtrochanteric and femoral shaft fractures have been treated with the help of intramedullary rods or nails, which are inserted into the marrow canal of the femur to immobilize the femur parts involved in fractures.
As shown in FIG. 9, a long bone 20 is shown in the form of a femur. The femur 20 is typical of long bones and includes a central shaft portion known as a diaphysis 24 as well as opposed portions extending from the diaphysis 24. The opposed portions include a proximal end portion know as a proximal epiphysis 26 and a distal end portion where know as a distal epiphysis 28. The femur 20 further includes a transition zone know as a proximal metaphysis 30 positioned between the diaphysis 24 and the proximal epiphysis 26. A transition zone know as a distal metaphysis 32 is positioned between the diaphysis 24 and the distal epiphysis 28. The proximal epiphysis 26 includes a neck 34 from which a head 36 extends. A hump on the outer periphery of the proximal epiphysis 26 to which tissue is attached is known as a greater trochanter 38 and is opposed to the head 36 and neck 34. A central recess in the end of the distal epiphysis 28 is known as a piriformis fossa 40. The femur 20 includes a harder outer layer of bone called cortical bone 42. The cortical bone 42 defines a first external cortical wall 44 and an opposed second external cortical wall 46. Softer cancellous bone 48 is found in bone canal 22, interior of the cortical bone 42.
Referring now to FIG. 10 a prior art intramedullary nail 50 is shown. The intramedullary nail 50 includes a cylindrical body 52. A first set of transverse openings 53 are positioned near proximal or first end 54 of the intramedullary nail 50 and a second set of transverse openings 55 are positioned near distal or second end 56 of the intramedullary nail 50. A single angled cross-nail or locking screw (not shown) is inserted through the femur into the first set of transverse openings 53 in the proximal end 54 of the intramedullary nail 50 to secure the nail 50 axially in the bone canal. In some varieties, one or two screws may also be inserted through the femoral shaft and through the second set of transverse openings 55 in the distal end 56 of the intramedullary nail 50. The prior art intramedullary nail 50 has been successfully employed in treating fractures in femurs.
Intramedullary nails typically have a generally cylindrical cross section and may be cannulated. The intramedullary canals of long bones of humans such as femurs have a shape that varies from person to person. The intramedullary canals of femurs have an arc or bow in the anterior posterior plane. Intramedullary nails, such as femoral nails, are available with a bowed shape based on anatomical statistics to account for the bow of the human intramedullary canal. Femoral nails are typically inserted in the bone through the proximal epiphysis of the long bone, with the entry point positioned either centrally, through the piriformis fossa, or on a side, through the greater trochanter. Femoral nails are typically either in the form of a piriformis fossa nail, with a generally linear proximal end portion for insertion through the piriformis fossa, or in the form of a greater trochanter nail, with a generally curved proximal end portion for insertion through the greater trochanter. The linear proximal end portions and the curved proximal end portions that are shaped to account for the insertion of the nail in the piriformis fossa and the greater trochanter, respectively, compromise the otherwise anatomical shape of the nail when fully inserted and often result in an improper fit. As a result, in spite of efforts to provide an anatomical intramedullary nail, anatomical differences from patient to patient result in nails often failing to fit properly in the canal. If a nail does not match the human bone canal, the nail may impart thigh pain while the implant is in the human bone canal. Further, each of these two separate nail configurations needs to be manufactured and made available for surgeries. Therefore, it would be advantageous to provide a nail that could be easily modified to fit the patient.